In the mid-19th century, a number of biological and social scientists came to believe that the genetic quality of the populations of the Western nations was deteriorating due to the relaxation of natural selection, the process by which nature eliminates the unfit in each generation by reducing their fertility and by early death. This view, and the idea that steps needed to be taken to correct the situation, came to be widely accepted by the first half of the 20th century. In the second half of the century, however, a reaction against eugenics set in, and from the 1970s onwards eugenics was almost universally dismissed. In this book, Richard Lynn reviews the history of the eugenics movement and seeks to rehabilitate the argument that genetic deterioration is occurring.